The present invention relates to abnormality detection for fuel reservoirs, and, more particularly, to methods and apparatuses for detecting abnormalities in fuel reservoirs of fuel vapor purge systems.
Generally, a vehicle provided with a reservoir for volatile liquid fuel includes a fuel vapor purge system. A typical fuel vapor purge system supplies fuel vapor generated in the fuel reservoir to a canister. The fuel vapor is temporarily retained in the canister and is purged (discharged) from the canister to an intake passage of the engine at an appropriate timing. In many cases, an apparatus for abnormality detection is incorporated in the fuel vapor purge system to detect a leakage caused by a puncture or rupture. This makes the system more reliable.
A fuel vapor purge system provided with a typical abnormality detection apparatus includes at least:
(1) an atmospheric air inlet valve, which controls introduction of atmospheric air from an upstream section of the engine""s intake passage to the canister;
(2) a purge control valve, which controls purging of fuel vapor from the canister to a downstream section of the intake passage;
(3) a differential pressure type reservoir pressure control valve, which supplies fuel vapor from the fuel reservoir to the canister if the difference between the pressure in the fuel reservoir and the pressure in the canister exceeds a predetermined level; and
(4) a canister inlet valve (also referred to as xe2x80x9cnegative pressure supply valvexe2x80x9d), which connects the canister to the fuel reservoir when necessary. In a communication passage that connects the fuel reservoir to the canister, a path that passes through the reservoir pressure control valve is parallel with a path that passes through the canister inlet valve.
The fuel vapor purge system initiates an abnormality detection procedure if two initial conditions are satisfied. More specifically, the first condition is that the engine coolant temperature must reach a procedure initiating level (for example, 80 degrees Celsius) when purging (introducing atmospheric air to the canister while discharging fuel vapor from the canister) is being performed. The second condition is that the pressure in the fuel reservoir must have been constant for a predetermined time period before the canister inlet valve is opened. When these conditions are met, the abnormality detection procedure is initiated.
First, the atmospheric air inlet valve is closed and the open/closed valve is opened. In this state, the fuel vapor purge system""s evaporation path, which includes the canister and the fuel reservoir, is entirely depressurized through the purge control valve. When the pressure in the evaporation path is lowered to a predetermined level, which is relatively low, the purge control valve is closed to seal the evaporation path. In the sealed state, the pressure in the evaporation path rises as time elapses. It is thus judged whether the evaporation path has a leak caused by a puncture or a rupture according to the rate at which the pressure in the evaporation path rises from the predetermined, relatively low level.
However, this abnormality detection procedure for the fuel vapor purge system has the following problem.
When the two initial conditions are met, the atmospheric air inlet valve is closed while the canister inlet valve is opened, thus decreasing the pressure in the evaporation path. However, in this state, the pressure in the fuel reservoir is applied to the canister through the canister inlet valve, which is open. This increases the time required for the pressure in the entire evaporation path, which includes the fuel reservoir and the canister, to fall to the predetermined low level. In other words, the pressure in the entire evaporation path does not reach the predetermined low level immediately after the detection procedure is started. Accordingly, the first cycle of the abnormality detection procedure is delayed.
Accordingly, it is an objective of the present invention to provide a method for detecting an abnormality in a fuel reservoir of a fuel vapor purge system separately from the remainder of the system with an increased accuracy and at a relatively early stage before or immediately after starting of the engine, and an apparatus for performing abnormality detection in accordance with this method.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, the invention provides a method for testing whether an abnormality exists in a fuel vapor purge system. The purge system has a line that connects an intake passage of an engine to a fuel reservoir and a canister inlet valve. The method includes sealing the fuel reservoir by closing the canister inlet valve after a cold start of the engine is performed or before the engine is started, measuring the pressure in the fuel reservoir in the sealed state, comparing the absolute value of the difference between the pressure in the fuel reservoir and the atmospheric pressure with a predetermined reference value, judging whether or not the fuel reservoir is abnormal in accordance with the result of the comparison, and performing an abnormality test on the fuel vapor purge system with negative pressure supplied from the intake passage to the line of the fuel vapor purge system if it is determined that the fuel reservoir has an abnormality.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.